89 lines
2.4 KiB
Plaintext
89 lines
2.4 KiB
Plaintext
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'\" Copyright (c) 1993 The Regents of the University of California.
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'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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.TH if n "" Tcl "Tcl Built-In Commands"
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.so man.macros
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.BS
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'\" Note: do not modify the .SH NAME line immediately below!
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.SH NAME
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if \- Execute scripts conditionally
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.SH SYNOPSIS
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\fBif \fIexpr1 \fR?\fBthen\fR? \fIbody1 \fBelseif \fIexpr2 \fR?\fBthen\fR? \fIbody2\fR \fBelseif\fR ... ?\fBelse\fR? ?\fIbodyN\fR?
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.BE
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.SH DESCRIPTION
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.PP
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The \fIif\fR command evaluates \fIexpr1\fR as an expression (in the
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same way that \fBexpr\fR evaluates its argument). The value of the
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expression must be a boolean
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(a numeric value, where 0 is false and
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anything is true, or a string value such as \fBtrue\fR or \fByes\fR
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for true and \fBfalse\fR or \fBno\fR for false);
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if it is true then \fIbody1\fR is executed by passing it to the
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Tcl interpreter.
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Otherwise \fIexpr2\fR is evaluated as an expression and if it is true
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then \fBbody2\fR is executed, and so on.
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If none of the expressions evaluates to true then \fIbodyN\fR is
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executed.
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The \fBthen\fR and \fBelse\fR arguments are optional
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.QW "noise words"
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to make the command easier to read.
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There may be any number of \fBelseif\fR clauses, including zero.
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\fIBodyN\fR may also be omitted as long as \fBelse\fR is omitted too.
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The return value from the command is the result of the body script
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that was executed, or an empty string
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if none of the expressions was non-zero and there was no \fIbodyN\fR.
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.SH EXAMPLES
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.PP
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A simple conditional:
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.PP
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.CS
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\fBif\fR {$vbl == 1} { puts "vbl is one" }
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.CE
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.PP
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With an \fBelse\fR-clause:
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.PP
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.CS
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\fBif\fR {$vbl == 1} {
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puts "vbl is one"
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} \fBelse\fR {
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puts "vbl is not one"
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}
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.CE
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.PP
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With an \fBelseif\fR-clause too:
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.PP
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.CS
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\fBif\fR {$vbl == 1} {
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puts "vbl is one"
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} \fBelseif\fR {$vbl == 2} {
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puts "vbl is two"
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} \fBelse\fR {
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puts "vbl is not one or two"
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}
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.CE
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.PP
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Remember, expressions can be multi-line, but in that case it can be a
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good idea to use the optional \fBthen\fR keyword for clarity:
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.PP
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.CS
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\fBif\fR {
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$vbl == 1
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|| $vbl == 2
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|| $vbl == 3
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} \fBthen\fR {
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puts "vbl is one, two or three"
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}
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.CE
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.SH "SEE ALSO"
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expr(n), for(n), foreach(n)
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.SH KEYWORDS
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boolean, conditional, else, false, if, true
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'\" Local Variables:
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'\" mode: nroff
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'\" End:
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